Step 1: Know Article 23.
Article 23 of the Constitution bans human trafficking, begar and forced labour. It protects weak sections from exploitation.
Step 2: Understand the case background.
In People's Union for Democratic Rights (PUDR) v. Union of India, workers on Asian Games projects were paid below the minimum wage.
Step 3: Note the ruling.
The Supreme Court held that when a person is forced by poverty to work for less than the minimum wage, it is forced labour under Article 23.
Step 4: See the expansion.
The Court widened forced labour to include economic compulsion, not just physical force. This grew the scope of Article 23.
Step 5: Rule out wrong options.
Vishaka dealt with sexual harassment, M.C. Mehta v. State of Tamil Nadu dealt with child labour, and Glaxo Laboratories dealt with labour court matters. None expanded Article 23 like PUDR.
Step 6: Final answer.
The landmark case is PUDR v. Union of India.
\[ \boxed{\text{PUDR v. Union of India}} \]